The lithium aluminate used hitherto in fuel cells is produced by annealing of a mixture of aluminum oxide and lithium carbonate. This is shown in French Pat. No. 1 502 000 and German OS No. 2 238 137. This know process is based on a solid state reaction and thus has certain difficulties inherent in this type of reaction; to wit the reaction speed is determined by the diffusion. Therefore, expensive measures are needed for the comminution and mixing of the reactants; i.e., homogenization of the mixture, and long reaction times. These difficulties make the adaptation of the above-mentioned known process to an industrial scale seem unprofitable.
According to another known process described in literature, .beta.-LiAl0.sub.2 may be produced by high pressure-high temperature synthesis from lithium peroxide and aluminum oxide. This is described in C. H. Chang, J. L. Margrave, J. Amer. Chem. Soc. Vol. 90, pp. 2020-2022 (1968). This type of production, however, is only of scientific or theoretical interest and, as with the case of the previously mentioned known method, it is unsuitable for utilization on an industrial scale.
A further possibility is to precipitate from an alkaline solution, acid or basic lithium aluminates, for example, of the composition LiH(Al0.sub.2).sub.2.5H.sub.2 O. See E. T. Allen, H. F. Rogers, J. Amer. Chem. Soc. Vol. 24 p. 304 (1900) or D. Prociv. Coll. Czech. Chem. Comm. Vol 1, pp. 8,95 (1929). Also, Li.sub.2 O.2Al.sub.2 O.sub.3.nH.sub.2 O may be precipitated as shown in N. P. Kozupalo et al, Redk. Shchelochnye Elem. Sb. Dokl. Vses Sovesch 2nd. Novosibirsk 1964 (publ. 1967) pp. 92-99 or H. A. Horan, J. B. Damiano, J. Amer. Chem. Soc. Vol 57 p. 2434 (1935).
Conversion is carried out by annealing at about 500.degree. C. into .alpha.-LiAl0.sub.2 and at about 800.degree. C.-900.degree. C. into .gamma.-LiAl0.sub.2. In order to arrive at the desired .beta.-modification, the precipitate with the composition Li.sub.2 O.2Al.sub.2 O.sub.3.nH.sub.2 O must first be treated for 7-10 days with a highly concentrated sodium hydroxide solution. The compound Li.sub.2 O.Al.sub.2 O.sub.3.nH.sub.2 O thus obtained may be converted by annealing into .beta.-LiAl0.sub.2. See V. A. Kolesova et al, Zh. Neorg. Khim. Vol 12, pp. 3220-3222 (1967) or J. S. Lileev et al, Zh. Neorg. Chim. Vol. 13, pp. 412-416 (1968).